Epoxy resins based on tetraglycidyl diamines

ABSTRACT

Novel tetraglycidates have the formula ##STR1## wherein R 1  and R 2  are independently hydrogen, alkyl of 1 to 8 carbon atoms, perfluoroalkyl, or cycloalkylidene of 5 to 7 carbon atoms. Epoxy resin systems exhibiting good tensile properties and moisture sensitivity can be made by copolymerizing the tetraglycidates with a polyamine curing agent. Prepregs can be made by combining the epoxy resin systems with a fiber reinforcement. The epoxy resin system may include a co-epoxide.

This is a division of application Ser. No. 835,735, filed Mar. 3, 1986,now U.S. Pat. No. 4,721,799.

FIELD OF THE INVENTION

This invention relates to novel bis(4,4'-aminophenoxy)-2,2-diphenylalkyltetraglycidates, to epoxy resin systems made from the noveltetraglycidates, to prepregs made using the epoxy resin systems, and toarticles of manufacture which incorporate the epoxy resins or theprepregs.

BACKGROUND OF THE INVENTION

Polyglycidates (also referred to herein as epoxy compounds) generallyconstitute a class of compounds having at least two glycidyl groups, thereactive moiety in each glycidyl group being the epoxy group.

Many epoxy compounds are commercially available for use in epoxy resinsystems including N,N,N',N',-tetraglycidyl-4,4'-methylene dianiline,having the structure ##STR2## This material is made by reacting anexcess of epichlorohydrin with methylene dianiline. It is availablecommercially as MY-720 from Ciba Geigy Corp., Ardsley, N.Y. and consistsof about 70% by weight of the above tetraglycidate, the remainder beingoligomers and triglycidates.

Another commonly used epoxy compound is made by reacting bisphenol Awith epichlorohydrin. Commercially available resins made from thisreaction contain the structure ##STR3## and include DER 331 from DowChemical and EPON® 828 (registered trademark) from Shell.

Epoxy groups are reactive to amine and hydroxyl functionalities and canthus be copolymerized (i.e. cured) with compounds containing suchfunctionalities to make epoxy resin systems. Generally polyamines arefavored as curing agents although polyhydroxy curing agents are alsowell known. The epoxy compounds can be reacted with one or more curingagents such that they are crosslinked, thereby finding use as structuraladhesives or as encapsulating materials for electronic components.

Epoxy resin systems are often used in prepregs, ready-to-mold materialscomprising fibrous reinforcement impregnated with uncured or partiallycured epoxy resin systems. Prepregs can be assembled into a final part(such as an airplane wing) and fully cured (C-staged) to form a finishedproduct. Such prepregs find wide use in the aircraft and aerospaceindustries.

Key properties of epoxy resin systems are tensile properties andmoisture sensitivity. High tensile strength is desirable in, forexample, structural adhesives. Low moisture sensitivity is alsodesirable since it leads to improved performance under hot/wetconditions.

Most advanced composites are fabricated from prepreg. Resin systemscontaining an epoxy compound such as MY-720 and aromatic amine hardenerare often used in prepreg since they possess the balance of propertiesrequired for this material. State-of-the-art epoxy/carbon fibercomposites have high compressive strengths, good fatiguecharacteristics, and low shrinkage during cure. However, since mostepoxy formulations used in prepreg are brittle, these composites havepoor impact resistance. In addition, epoxy formulations absorb moisturewhich reduces their high temperature properties and affects theirdimensional ability.

Thus, new epoxy compounds which could be used to make epoxy resinsystems which improve such desirable physical and mechanical properties,relative to present state-of-the-art epoxy systems, would be a usefuladdition to the structural adhesive, airplane, aerospace, and other likeart areas.

THE INVENTION

The present invention provides, in one aspect, novel tetraglycidates ofthe formula ##STR4## wherein R¹ and R² are independently hydrogen, alkylof 1 to 8, preferably 1 to 4, carbon atoms, or perfluoroalkyl. ##STR5##taken together may also form a cycloalkylidene ring of from 5 to 7carbon atoms such as cyclopentylidene, cyclohexylidene, andcycloheptylidene. R¹ and R² are most preferably methyl groups ortrifluoromethyl groups.

In another aspect the invention provides novel epoxy resin systemscomprising a tetraglycidate having the above formula (I) copolymerizedwith a polyamine curing agent (also referred to herein as a hardener).The polyamine hardener may, for example, be any of the well knownaliphatic polyamines such as diethylene triamine, triethylenetetraamine, or tetraethylene pentaamine. Additional hardeners are thosecontaining benzenoid unsaturation such as m- and p-phenylenediamine,1,6-diaminonaphthalene, 4,4'-diaminodiphenylmethane (also known as4,4'-methylene dianilene), 4,4'-diaminodiphenyl ether, sulfanilamide,3-methyl-4-aminobenzamide, and 4,4'-diaminodiphenyl sulfone (DDS),4,4'-diaminodiphenyl, ring-alkylated derivatives of m-phenylene diaminesuch as ETHACURE® 100 from Ethyl Corp., Baton Rouge, LA, and the like.Another useful class of polyamine curing agents are those disclosed inU.S. Pat. No. 4,521,583, which have the formula ##STR6## wherein a is 2or 3, R³ is hydrogen, alkyl of 1 to 8 carbon atoms or aryl of 6 to 18carbon atoms, and X is a divalent or trivalent organic hydrocarbon,hetero-interrupted hydrocarbon, or substituted hydrocarbon radical or##STR7## These hardening agents may be prepared from correspondingstarting materials, e.g. nitro compounds, by reduction, for example,according to methods described in U.K. Pat. No. 1,182,377. Particularlycontemplated are those compounds (II) wherein R³ is hydrogen or C₁ -C₃alkyl and X is a divalent or trivalent radical selected from

(1) divalent groups consisting of --(CH₂)_(y) -- wherein y is an integerof from 2 to 12, --CH₂ CH₂ OCH₂ CH₂ OCH₂ CH₂ --, ##STR8##

(2) trivalent groups of the formula ##STR9## wherein n and m are thesame or different integers from 1 to 4.

Preferred curing agents are (i) DDS, (ii) those diamines having theformula ##STR10## wherein each of the two amino groups is meta or parato the carbonyl group bonded to the same ring and wherein Y is

    --(CH.sub.2).sub.q --

wherein q is an integer from 2 to 12, preferably 2 to 6, and mostpreferably 3: ##STR11## wherein t is an integer of from 0 to about 5;and ##STR12##

The polyamine curing agent and epoxy compound are mixed essentially inan amount which provides about 0.3 to about 2.0, preferably about 0.4 to1.7, and most preferably about 0.45 to about 1.3 moles of amine hydrogenfor each mole of epoxy groups. The epoxy resin system comprising thecuring agent and epoxy compound may be cured by heating between about200-400° F. for time periods ranging between about 0.5 and about 12hours.

In another aspect, this invention provides prepregs comprising the novelepoxy resins described herein. Prepregs contain structural fibers. Thestructural fibers which are useful in this invention include carbon,graphite, glass, silicon carbide, poly(benzothiazole),poly(benzimidazole), poly(benzoxazole), alumina, titania, boron, andaromatic polyamide fibers. These fibers are characterized by a tensilestrength of greater than 100,000 psi, a tensile modulus of greater thantwo million psi, and a decomposition temperature of greater than 200° C.The fibers may be used in the form of continuous tows (500 to 400,000filaments each), woven cloth, whiskers, chopped fiber or random mat. Thepreferred fibers are carbon and graphite fibers, aromatic polyamidefibers, such as Kevlar 49 fiber (obtained from E. I. duPont de Nemours,Inc., Wilmington, DE), and silicon carbide fibers.

The epoxy resin in this invention is prepared by standard methods, suchas that described in U.S. Pat. No. 2,951,822 and also in an article byW. T. Hodges et al., SAMPE Quarterly, October 1985, pages 21-25, both ofwhich are incorporated herein by reference. The method entails reactingan aromatic diamine with a four to twenty molar excess ofepichlorohydrin at elevated temperature, generally 50° to 100° C. Thisis followed by dehydrochlorination of the intermediate chlorohydrinamine with aqueous base. The product is then isolated by diluting with awater immiscible solvent, washing with water, drying with a suitabledesicant, and concentrating to obtain a resinous product. The epoxidethus obtained generally is found by titration to contain 70 to 90% ofthe theoretical amount of epoxy groups. This is due to formation ofoligomeric residues and/or incomplete reaction of the monomeric diaminewith epichlorohydrin. For example, Kirk-Othmer Encyclopedia of ChemicalTechnology, 3rd edition, Volume 9, page 277, gives the epoxy equivalentweight (EEW) of MY-720 (a commonly used commercial glycidyl amine as117-133. The theoretical EEW is 105. The materials are furthercharacterized by liquid chromatography, infrared spectroscopy, andnuclear magnetic resonance.

Epoxy resin systems are prepared by heating and stirring the epoxy resinto 60° to 120° C. and adding the hardener. If the hardener is a solid,it is preferably added as a fine powder. An inert diluent such asN,N-dimethyl formamide or N-methylpyrrolidone may be used if desired.Reaction of the epoxy and hardener occur as the mixture is heated. Forprepreg, the mixture is B-staged or partially reacted (i.e. typically 3to 15 percent of the epoxy groups are reacted) in order to obtain aresin system with the required physical properties (i.e. viscosity andtack).

Prepregs according to the present invention can be made by embeddingfilaments or fibers into, or by coating woven or non-woven webs,rovings, tows, or the like, with a curable epoxy resin resin matrixwhich is ultimately manipulated and cured to a solid composite.Particular selection of the filament, fiber, or textile material, epoxycompound, and curing agent can give a range of curable composites whichcan be tailored to suit a given need or application.

It is preferred to apply the resin as a hot melt to the fiberreinforcement. The B-staged epoxy resin system may conveniently first beapplied to long sheets of differential release paper, i.e. paper towhich a release agent such as any of several of the siliconeformulations well known in the art, has been applied. In a prepregmachine, resin coated on the release paper is transferred to a web offiber. This is done by sandwiching the web between plies of coatedrelease paper and passing the material through a set of heated rollers.The resulting prepreg is then cooled and taken up on a spool. The totalamount of resin applied to the fiber reinforcement is preferably betweenabout 20 and about 50 wt. percent of resin solids based on the weight ofthe uncured composite. If desired, the prepreg may at this point becooled to 0° F. or less by exposure to any convenient cryogenic material(such as dry ice) for shipping or storage.

Upon rewarming to about room temperature, the prepreg can then be usedto make structural parts such as airplane wings or fuselage components.The prepreg may also be used to make other useful articles such as golfshafts, tennis rackets, musical instruments, satellite components, androcket motors. To make useful articles from prepreg the prepreg may becut into strips and then laid up (e.g. on a mold surface) to create thedesired shape. The shaped, layered composite is then fully cured atpressures between about atmospheric to about 500 psi and temperaturesbetween about 100° C. to about 300° C. in an oven, autoclave, or heatedpressure mold. Depending on the exact epoxy formulation, temperature,and pressure, curing times may range between about 0.2 and about 8hours, the optimum time, pressure, and temperature being easilyascertainable by means of trial runs. This final cure essentiallyC-stages the composite, meaning that the resin has substantially reachedthe final stage of polymerization where crosslinking becomes general andthe composite is substantially infusible.

When making the epoxy resin system for use generally or for usespecifically as a prepreg, a modifying thermoplastic polymer, polymerblend, or elastomer may be used to adjust the viscosity of the resin andto desirably enhance processability and mechanical properties,particularly toughness and damage tolerance. The classes of resins whichare broadly useful include poly(aryl ether) resins as disclosed, forexample, in U.S. Pat. Nos. 4,175,175 and 4,108,837 and exemplified bythermoplastic poly(aryl ether sulfones) available commercially under theregistered trademark UDEL® from Union Carbide Corporation,polyetherimides available, for example, under the registered trademarkULTEM® from General Electric, phenoxy resins (of the type commerciallyavailable under the registered trademark UCAR® from Union CarbideCorporation), polyurethanes, butadiene/styrene/acrylonitrileterpolymers, nylons, butadiene/acrylonitrile liquid rubbers such asHYCAR® CTBN from B. F. Goodrich and the like. The amount ofthermoplastic resin employed will generally fall in a range of about 1to about 30 wt. % based on the weight of the epoxy resin system,although amounts above or below this range may be desired in certainapplications. Preferred thermoplastic resins include poly(aryl ethersulfones), polyetherimides, phenoxy resins, and butadiene/acrylonitrileliquid rubbers. The thermoplastic resin is generally added to the epoxycompound and mixed therewith prior to addition of the polyamine curingagent. The modifier will often be miscible with the epoxy compound,although it will also often be occluded as a dispersion within the finalcured epoxy resin once the resin is thermoset.

Co-epoxides may also be used in the epoxy resin system. The co-epoxycompounds (or resins), when employed, may be present in an amount up toabout 40 wt. %, preferably up to about 30 wt. %, based on the amount of(cured or uncured) tetraglycidate used.

Co-epoxy compounds which may be used herein contain two or more epoxygroups having the following formula: ##STR13## The epoxy groups can beterminal epoxy groups or internal epoxy groups. The epoxides are of twogeneral types: polyglycidyl compounds or products derived fromepoxidation of dienes or polyenes. Polyglycidyl compounds contain aplurality of 1,2-epoxide groups derived from the reaction of apolyfunctional active hydrogen containing compound with an excess of anepihalohydrin under basic conditions. When the active hydrogen compoundis a polyhydric alcohol or phenol, the resulting epoxide compositioncontains glycidyl ether groups. A preferred group of polyglycidylcompounds are made via condensation reactions with2,2-bis(4-hydroxyphenyl) propane, also known as bisphenol A, and havestructures such as III, ##STR14## where n has a value from about 0 toabout 15. These epoxides are bisphenol-A epoxy resins. They areavailable commercially under the trade names such as "Epon 828," "Epon1001," and "Epon 1009" from Shell Chemical Co. and as "DER 331", "DER332", and "DER 334" from Dow Chemical Co. The most preferred bisphenol Aepoxy resins have an "n" value between 0 and 10.

Polyepoxides which are polyglycidyl ethers of 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenyl sulfone, 4,4'-biphenol,4,4'-dihydroxydiphenyl sulfide, phenolphthalein, resorcinol,4,2'-biphenol, or tris(4-hydroxyphenyl) methane and the like, are usefulin this invention. In addition, EPON 1031 (a tetraglycidyl derivative of1,1,2,2-tetrakis(hydroxyphenyl)ethane from Shell Chemical Company), andApogen 101, (a methylolated bisphenol A resin from Schaefer ChemicalCo.) may also be used. Halogenated polyglycidyl compounds such as D.E.R.542 (a brominated bisphenol A epoxy resin from Dow Chemical Company) arealso useful. Other suitable epoxy resins include polyepoxides preparedfrom polyols such as pentaerythritol, glycerol, butanediol ortrimethylolpropane and an epihalohydrin.

Polyglycidyl derivatives of phenol-formaldehyde novolaks such as IVwhere n=0.1 to 8 and cresol-formaldehyde novolaks such as V where n=0.1to 8 are also useable. ##STR15## The former are commercially availableas D.E.N. 431, D.E.N. 438, and D.E.N. 485 from Dow Chemical Company. Thelatter are available as, for example, ECN 1235, ECN 1273, and ECN 1299(obtained from Ciba-Geigy Corporation, Ardsley, NY). Epoxidized novolaksmade from bisphenol A and formaldehyde such as SU-8 (obtained fromCelanese Polymer Specialties Company, Louisville, KY) are also suitable.

Other polyfunctional active hydrogen compounds besides phenols andalcohols may be used to prepare the polyglycidyl adducts useful in thisinvention. They include amines, aminoalcohols and polycarboxylic acids.

Adducts derived from amines include N,N-diglycidyl aniline,N,N-diglycidyl toluidine, N,N,N', N'-tetraglycidylxylylene diamine,(i.e., VI) N,N,N', N'-tetraglycidyl-bis (methylamino) cyclohexane (i.e.VII), N,N,N'N'-tetraglycidyl-4,4'-methylene dianiline, (i.e. VIII)N,N,N',N'-tetraglycidyl-3,3'-diaminodiphenyl sulfone, andN,N'-dimethyl-N,N'-diglycidyl-4,4'-diaminodiphenyl methane. Commerciallyavailable resins of this type include Glyamine 135 and Glyamine 125(obtained from F.I.C. Corporation, San Francisco, CA.), Araldite MY-720(obtained from Ciba Geigy Corporation) and PGA-X and PGA-C (obtainedfrom the Sherwin-Williams Co., Chicago, Illinois). ##STR16##

Suitable polyglycidyl adducts derived from aminoalcohols includeO,N,N-triglycidyl-4-aminophenol, available as Araldite 0500 or Araldite0510 (obtained from Ciba Geigy Corporation) andO,N,N-triglycidyl-3-aminophenol (available as Glyamine 115 from F.I.C.Corporation).

Also suitable for use herein are the glycidyl esters of carboxylicacids. Such glycidyl esters include, for example, diglycidyl phthalate,diglycidyl terephthalate, diglycidyl isophthalate, and diglycidyladipate. There may also be used polyepoxides such as triglycidylcyanurates and isocyanurates, N,N-diglycidyl oxamides, N,N'-diglycidylderivatives of hydantoins such as "XB 2793" (obtained from Ciba GeigyCorporation), diglycidyl esters of cycloaliphatic dicarboxylic acids,and polyglycidyl thioethers of polythiols.

Other epoxy-containing materials are copolymers of acrylic acid estersof glycidol such as glycidyl acrylate and glycidyl methacrylate with oneor more copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidyl methacrylate, 1:1 methyl methacrylate-glycidylacrylate and 62.5:24:13.5 methyl methacrylate:ethyl acrylate:glycidylmethacrylate.

Silicone resins containing epoxy functionality, e.g.,2,4,6,8,10-pentakis[3-(2,3-epoxypropoxy)propyl]-2,4,6,8,10-pentamethylcyclopentasiloxaneand the diglycidyl ether of1,3-bis(3-hydroxypropyl)tertramethyldisiloxane) are also useable.

The second group of epoxy resins is prepared by epoxidation of dienes orpolyenes. Resins of this type include bis(2,3-epoxycyclopentyl) ether,IX, ##STR17## copolymers of IX with ethylene glycol which are describedin U.S. Pat. No. 3,398,102,5(6)-glycidyl-2-(1,2-epoxyethyl)bicyclo[2.2.1]heptane, X, anddicyclopentadiene diepoxide. Commercial examples of these epoxidesinclude vinycyclohexene dioxide, e.g., "ERL-4206" (obtained from UnionCarbide Corp.), 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, e.g., "ERL-4221" (obtained from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate, e.g., "ERL-4201" (obtained from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, e.g., "ERL-4289"(obtained from Union Carbide Corp.), dipentene dioxide, e.g., "ERL-4269"(obtained from Union Carbide Corp.)2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexanemetadioxane, e.g.,"ERL-4234" (obtained from Union Carbide Corp.) and epoxidizedpoly-butadiene, e.g., "Oxiron 2001" (obtained from FMC Corp.)

Other suitable cycloaliphatic epoxides include those described in U.S.Pat. Nos. 2,750,395; 2,890,194; and 3,318,822 which are incorporatedherein by reference, and the following: ##STR18##

Other suitable epoxides include: ##STR19## where n is 1 to 4, m is(5-n), and R is H, halogen, or C₁ to C₄ alkyl.

Reactive diluents containing one epoxide group such as t-butylphenylglycidyl ether, may also be used. The reactive diluent may comprise upto 25 percent by weight of the epoxide component.

The preferred co-epoxy resins are bisphenol A epoxy resins of formulaIII where n is between 0 and 5, epoxidized novolak resins of formula IVand V where n is between 0 and 3, N,N,N',N'-tetraglycidyl xylylenediamine, and diglycidyl pthalate.

The epoxy resin system may additionally contain an accelerator toincrease the rate of cure. Accelerators which may be used herein includeLewis acid:amine complexes such as BF₃.monoethylamine, BF₃.piperdine,BF₃.2-methylimidazole; amines, such as imidazole and its derivativessuch as 4-ethyl-2-methyl-imidazole, 1-methylimidazole,2-methylimidazole; N,N-dimethylbenzylamine; acid salts of tertiaryamines, such as the p-toluene sulfonic acid:imidazole complex, salts oftrifluro methane sulfonic acid, such as FC-520 (obtained from 3MCompany), organophosphonium halides, dicyandiamide 1,1-dimethyl-3-phenylurea (Fikure 62 U from Fike Chemical Co.), and chlorinated derivativesof 1,1-dimethyl-3-phenyl urea (monuron and diuron from du Pont). Ifused, the amount of cure accelerator may be from 0.02 to 10 percent ofthe weight of the epoxy resin system (i.e., epoxy plus hardener).

In addition to structural fibers, thermoplastic polymers, and cureaccelerators, the epoxy resin systems may also contain particulatefillers such as talc, mica, calcium carbonate, aluminum trihydrate,glass microballoons, phenolic thermospheres, pigments, dyes, and carbonblack. In prepregs, up to half of the weight of structural fiber in thecomposition may be replaced by filler. Thixotropic agents such as fumedsilica may also be used.

In the epoxy resin systems (i.e. epoxy plus hardener) of this invention,the proportion of epoxy resin can be about 95 to about 30 percent byweight, preferably about 80 to about 35 wt. percent, and the proportionof hardener can be from about 5 to about 70 wt. percent, preferablyabout 15 to about 60 wt. percent.

In prepregs and composites (epoxy plus hardener and structural fiber),the percent by weight of the epoxy resin system can be from about 20 to80 percent by weight, based on the weight of the prepreg or composite,preferably about 25 to about 60 wt. percent. The structural fibercomprises 80 to 20 wt. percent, preferably 75 to 40 wt. percent of thetotal composition.

The invention is further disclosed and described by means of thefollowing examples which are not to be taken as limiting.

EXAMPLE 1

This example described the synthesis of4,4'-bis(4,4'-aminophenoxy)-2,2-diphenylpropane tetraglycidate (BAPPTG)from 4,4'-bis(4,4'aminophenoxy)-2,2-diphenylpropane (BAPP) andepichlorohydrin.

BAPP (300.0 g), epichlorohydrin (800 ml), ethanol (350 ml), and 50 ml ofwater were placed into a 2 L three-neck round-bottom flask that wasequipped with a mechanical stirrer, addition funnel, and a thermometerthat was connected to a Therm-o-watch temperature controller. Themixture was placed under a blanket of nitrogen and heated to reflux withgentle stirring. The reaction mixture was a slurry initially but quicklybecame homogeneous as the reflux temperature was approached. After themixture had refluxed for 4 hours, the temperature was lowered to 60° C.and 300 g of 50% aqueous sodium hydroxide were added at such a rate thatthe temperature was maintained at 60° C. When addition was complete, thetemperature was held at 60° C. for 2 hours, at which time heating wasdiscontinued. When the mixture was at room temperature, the liquid wasdecanted from the flask into a separatory funnel. The large mass ofsodium chloride left behind was washed with methylene chloride (2×200ml) and these washings were added to the separatory funnel. Water (500ml) was added to the separatory funnel and the layers were separated.The organic phase was washed with water (2×300 ml) and brine (1×300 ml),dried (Na₂ SO₄), filtered, and the filtrate was concentrated on a rotaryevaporator (50 mm Hg., at 80° C., the 0.1 mm Hg at 80° C.). 400 g (95%)of a light brown viscous liquid were obtained. Physical Data: Epoxyequivalent weight=165 g/mol (Theory EEW=158 g/mol).

EXAMPLE 2

This example describes the preparation of unreinforced castings ofBAPPTG and a polyamine curing agent having the formula ##STR20## andherein designated by the acronym DADE.

86.0 of the epoxy of Example 1 was heated to 100° C. in a three-neck 500ml round-bottom flask fitted with a thermometer connected to aTherm-o-watch temperature controller and a mechanical stirrer. 42.0 g ofDADE was added. After the temperature came back to 100° C., all thediamine dissolved after another 15-45 minutes. Vacuum (50 mm Hg) wasapplied for about 5 minutes, stirring was discontinued and the vacuumwas applied for 5 minutes more. The resin was then poured into a mold(dimensions 8"×10"×1/8") which had been warmed in a 90° C. oven. Thecasting was cured as follows: 75° C. (4 hours) → 4 hours → 120° C. (2hours) → 2 hours → 179° C. (2 hours).

Glass transition temperatures were determined on a DuPont 982 thermalanalyzer as the maximum of the loss modulus peak of a DMA scan. Watersensitivity was determined by soaking a 2.0"×0.5"×1/8" coupon in waterfor 2 weeks at 71.1° C. (160° F.). The percent weight gain of the couponwas determined after soak.

Control A

This example is comparative and describes the preparation ofunreinforced castings from an epoxy resin having the trade designationMY-720 and having as its major constituent a compound of the formula##STR21##

100 g of MY-720 was placed in a three-neck round-bottom flask equippedwith a mechanical stirrer, thermometer fitted with a Therm-o-watchtemperature controller, and a gas adaptor. The epoxy was warmed to 110°C., at which time 61 g of DADE were added. Heating was continued untilthe DADE was completely dissolved. Vacuum (50 mm Hg) was applied, andafter 5 minutes stirring was stopped, the heating mantle was removed,and the vacuum was continued 5 more minutes. The resin was poured into a8"×10"×1/8" mold that was prewarmed in a 100° C. oven.

Table I lists physical data for the castings of Example 2 and Control A

                  TABLE I                                                         ______________________________________                                        PROPERTIES OF UNREINFORCED CASTINGS                                                       Example 2   Control A                                             ______________________________________                                        Composition.sup.a                                                                           BAPPTG    86.0 g  MY-720 100 g                                                DADE      42.0 g  DADE   61 g                                   Tensile Properties.sup.c                                                      Tensile Strength                                                                            14.5          10.5                                              (ksi)                                                                         Tensile Modulus                                                                             498           404                                               (ksi)                                                                         Elongation (%)                                                                              5.0           3.8                                               Tg (°C.) Dry                                                                         188           210                                               Wet.sup.b     155           173                                               Water Uptake (%).sup.b                                                                      2.3           3.4                                               ______________________________________                                         .sup.a NH/epoxide stoichiometry = 1.0/1.0                                     .sup.b Measured after soaking in water for two weeks at 71.1° C.       (160° F.).                                                             .sup.c ASTM D638                                                         

It is apparent that compositions according to the invention havesuperior tensile strength, tensile modulus, elongation, and waterresistance compared to Control A.

EXAMPLE 3

This example describes the preparation of a thermosetting composition ofBAPPTG, 4,4' diaminodiphenylsulfone (DDS), and a reactive diluent.

37 g of DDS was added slowly to 40 g of diglycidylphthalate (GlyCel A100 from Celanese Corp.), at 100° C., with stirring. The mixture wasstirred at 100° C., for 1 hour, after which time 160 g of BAPPTG wereslowly added. When the resin was homogeneous, an unreinforced castingwas prepared in the same manner as described in Example 2. TheNH/epoxide stoichiometry was 0.5. This casting was tested for tensilestrength, modulus, and % elongation. Results are shown in Table II.

                  TABLE II                                                        ______________________________________                                                        Example 3                                                                     BAPPTG-160 g                                                  Casting         Gly-Cel A 100-40 g                                            Composition     DDS - 37 g                                                    ______________________________________                                         Tensile Properties                                                           Tensile strength (ksi)                                                                        4.3                                                           Tensile modulus (ksi)                                                                         566                                                           Elongation (%)  0.8                                                           ______________________________________                                    

Control B

A thermoset resin was prepared as in Example 3 with 40 g of Glycel A100, 48 g DDS, and 160 g of MY-720. This resin has the same NH/epoxidestoichiometry and weight ratio of epoxies as that of Example 3. Anunreinforced casting prepared as in Control A was too brittle to test.

EXAMPLE 4

This example describes the preparation of unreinforced castings ofBAPPTG, MY-720, and 4,4-diaminodiphenylsulfone.

75 g of the epoxy of example 1 and 75 g of MY-720 were heated to 100° C.in a 3-neck round bottom flask equipped with a paddle stirrer, and athermometer connected to a therm-o-watch temperature controller. 35 g ofDDS was slowly added with stirring. After the mixture had been heatedfor 90 minutes at 100° C., the diamine had dissolved. Then the resin wasdegassed and poured into a mole (8"×10"×1/8"). The casting was cured inthe same manner as Example 2.

Control C

This example is comparative and describes the preparation of anunreinforced casting of only M-720 and DDS.

A resin system containing 130 g of MY-720 and 35 g DDS was prepared andcured as in Example 4.

Table III lists the physical data for Example 4 and Control C.

                  TABLE III                                                       ______________________________________                                        PROPERTIES OF UNREINFORCED CASTINGS                                                       Example 4   Control C                                             ______________________________________                                        Composition   BAPPTG    75 g    MY-720 130 g                                                MY-720    75 g    DDS    35 g                                                 DDS       35 g                                                  Tensile Properties.sup.a                                                      Tensile Strength                                                                            4.7           4.5                                               (ksi)                                                                         Tensile Modulus                                                                             472           454                                               (ksi)                                                                         Elongation (%)                                                                              1.0           1.0                                               ______________________________________                                         .sup.a ASTM D638                                                         

EXAMPLE 5

This example describes the preparation of undirectional epoxy/graphiteprepreg.

A thermosetting composition like that of Example 2 was prepared byblending 1500 g of BAPPTG (EEW=175) and 672 g of the diamine DADE at100° C. for approximately 90 minutes. At this point a 1.5 mil film wascast and was determined to have appropriate tack for prepreg. It wascoated on 13.5 inch wide release paper (type 2-60-SF-157 and 168A,obtained from Daubert Coated Products Dixon, IL) at a coating weight of110 g/m².

Twelve-inch wide undirectional prepreg tape was made by forming a ribbonof 78 tows of carbon fiber and contacting it between 2 plies ofepoxy-coated release paper in a prepreg machine. In the prepreg machine,the sandwich of fiber and coated release paper passed over a series ofheated rollers to melt the resin into the fibers. The finished tapecontained about 64 percent by weight of fiber. Its thickness was about0.007 inches. The fiber was a polyacrylonitrile-based fiber with atensile strength of 5.5×10⁵ psi and a tensile modulus of 35×10⁶ psi.

Control D

This example is comparative and describes the preparation ofunidirectional epoxy/graphite prepreg.

A thermosetting composition like that of Control A was prepared byblending 1227 g of MY-720 and 773 g of DADE. The resin was advanced byheating for 100 minutes at 100° C. After the mixture cooled to 70° C.,it was coated on 13.5 inch wide release paper (type 2-60-SF-157 and168A, obtained from Daubert Coated Products Dixon, IL) at a coatingweight of 104 g/m².

Twelve-inch wide undirectional prepreg tape was made by forming a ribbonof 78 tows of carbon fiber and contacting it between 2 plies ofepoxy-coated release paper in a prepreg machine. In the prepreg machine,the sandwich of fiber and coated release paper passed over a series ofheated rollers to melt the resin into fibers. The finished tapecontained about 70 percent by weight of fiber. Its thickness was about0.007 inches. The fiber was a polyacrylonitrile-based fiber with atensile strength of 5.5×10⁵ psi and a tensile modulus of 35×10⁶ psi.

EXAMPLE 6

This example describes the cured unidirectional laminates made from theprepreg of Example 5.

The laminate was cured in an autoclave at 355° F. for 2 hours. Theautoclave pressure was 90 psi. Seven plies of prepreg were used to makethe specimen. Compressive properties were measured using a modifiedASTM-D695 procedure. Unidirectional graphite/epoxy tabs were added toprevent the sample ends from crushing. A gage length of approximately0.188 inches was used. End tabs on compressive samples were adheredusing FM-300 film adhesives (obtained from American Cyanamid Company,Havre de Grace, MD), which was cured at 177° C. for 1 hour. Thelongitudinal compressive strengths of unidirectional laminates ofExample 6 is shown in Table IV.

                  TABLE IV                                                        ______________________________________                                        LONGITUDINAL COMPRESSIVE STRENGTH (ksi)                                                  ROOM                                                                          TEMPERATURE     180° F.                                                                        180° F.                             CONDITION  (DRY)           (DRY)   (WET).sup.a                                ______________________________________                                        EXAMPLE 6  215             197     185                                        ______________________________________                                         .sup.a Specimens were soaked in water 2 weeks at 160° F. prior to      testing.                                                                 

For many applications a longitudinal compressive strength of at least150 ksi is required. The results in Table IV indicate that thecompositions of this invention possess excellent compressive strengthseven under hot/wet conditions.

EXAMPLE 7 and Control E

This example demonstrates the compressive strength after impact of aquasiisotropic laminate fabricated with the composition of thisinvention, a prepreg prepared as in Example 5, and with a control madewith prepreg prepared as in control D. The test employed measures thedamage tolerance of composites. The latter depends on the choice ofmatrix resin. Test specimens had dimensions of 6×4×approximately 0.2inches. The panels were impacted in the center with a Gardner typeImpact Tester (Gardner Laboratories, Bethesda, MD) having a 5/8 inchdiameter spherical indenter. The impact was normal to the plane of thefibers. When impacted, the laminate was simply supported over a 3 inchby 5 inch cut out in an aluminum plate with a plywood backup. Theimpacted panel was tested for residual compressive strength in a steelfixture that constrained the edges from out-of-plane buckling. Resultsare tabulated in Table V.

                  TABLE V                                                         ______________________________________                                        RESIDUAL COMPRESSIVE STRENGTH (in ksi psi)                                    AFTER IMPACT RESULTS.sup.a,b                                                  EXAMPLE 7     CONTROL E                                                       ______________________________________                                        27.2          19.3                                                            ______________________________________                                         .sup.a Cure schedule 2 hours at 355° F. Autoclave pressure 90 psi.     Layup: [+45/90/-45/0]35                                                       .sup.b IMPACT LEVEL 1500 INLB/IN                                         

It is clear that the residual compressive strength of a laminate madewith the composition of this invention is significantly higher than thatof the control. Thus, the fiber reinforced composites of this inventionhave improved impact resistance.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims.

What is claimed is:
 1. Epoxy resin systems comprising (a) atetraglycidate of the formula ##STR22## wherein R¹ and R² areindependently hydrogen, alkyl of 1 to 8 carbon atoms, perfluoroalkyl, or##STR23## taken together form a cycloalkylidene ring of 5 to 7 carbonatoms, and (b) a polyamine curing agent.
 2. An epoxy resin system asdefined in claim 1, wherein said polyamine is selected from the groupconsisting of m-phenylenediamine, p-phenylenediamine,1,6-diaminonaphthalene, 4,4'-diaminodiphenyl methane,4,4'-diaminodiphenyl ether, sulfanilamide, 3-methyl-4-aminobenzamide,4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl, and alkylatedderivatives of m-phenylenediamine.
 3. An epoxy resin system as definedin claim 1, wherein said polyamine has the formula ##STR24## wherein: ais 2 or 3;R³ is hydrogen, alkyl of 1 to 8 carbon atoms or aryl of 6 to18 carbon atoms; and X is a divalent or trivalent organic hydrocarbon,or ##STR25##
 4. An epoxy resin system as defined in claim 3, whereinR³is hydrogen, alkyl of 1 to 3 carbon atoms, or phenyl; and X is adivalent or trivalent radical selected from (1) divalent groupsconsisting of --(CH₂)₄ -- wherein y is an integer of from 2 to 12,##STR26## (2) trivalent groups of the formula ##STR27## wherein n and mare the same or different integers from 1 to
 4. 5. An epoxy resin systemas defined in claim 1, wherein said polyamine is selected from the groupconsisting of (i) 4,4'-diaminodiphenyl sulfone, (ii) diamines having theformula ##STR28## wherein each of the two amino groups is meta or parato the carbonyl group bonded to the same ring and wherein Y is

    --(CH.sub.2).sub.q --

wherein q is an integer from 2 to 12, ##STR29## wherein t is an integerof from 0 to about 5, and ##STR30##
 6. An epoxy resin system as definedin claim 5, wherein q is from about 2 to about
 6. 7. An epoxy resinsystem as defined in claim 6 wherein q is
 3. 8. An epoxy resin system asdefined in claim 1, wherein said polyamine curing agent is mixed withsaid tetraglycidate in an amount which provides about 0.3 to about 2.0moles of amine hydrogen for each mole of epoxy groups.
 9. An epoxy resinsystem as defined in claim 8, wherein said amount provides about 0.4 toabout 1.7 moles of amine hydrogen for each mole of epoxy groups.
 10. Anepoxy resin system as defined in claim 9, wherein said amount providesabout 0.45 to about 1.3 moles of amine hydrogen for each mole of epoxygroups.
 11. A prepreg, comprising:an epoxy resin system comprising atetraglycidate of the formula ##STR31## wherein R¹ and R² areindependently hydrogen, alkyl of 1 to 8 carbon atoms, perfluoroalkyl, or##STR32## taken together form a cycloalkylidene ring of 5 to 7 carbonatoms; a polyamine curing agent; and a fiber reinforcement.
 12. Aprepreg as defined in claim 11, wherein said polyamine is selected fromthe group consisting of (i) 4,4'-diaminodiphenyl sulfone, (ii) diamineshaving the formula ##STR33## wherein each of the two amino groups ismeta or para to the carbonyl group bonded to the same ring and wherein Yis

    --(CH.sub.2).sub.q --

wherein q is a integer from 2 to 12, ##STR34## wherein t is an integerof from 0 to about 5and ##STR35##
 13. A prepreg as defined in claim 12,wherein q is from about 2 to about
 6. 14. A prepreg as defined in claim13 wherein q is
 3. 15. A prepreg as defined in claim 11, wherein saidpolyamine curing agent is mixed with said tetraglycidate in an amountwhich provides about 0.3 to about 2.0 moles of amine hydrogen for eachmole of epoxy groups.
 16. A prepreg as defined in claim 15, wherein saidamount provides about 0.4 to about 1.7 moles of amine hydrogen for eachmole of epoxy groups.
 17. A prepeg as defined in claim 16, wherein saidamount provides about 0.45 to about 1.3 moles of amine hydrogen for eachmole of epoxy groups.
 18. A prepreg as defined in claim 11, wherein saidfiber reinforcement is a material selected from the group consisting ofglass, carbon, graphite, silicon carbide, boron, alumina, titania,poly(benzothiazole), poly(benzimidazole), poly(benzoxazole), andaromatic polyamide fibers.
 19. A prepreg as defined in claim 11, whereinsaid fiber reinforcement is in the form of continuous tows, woven cloth,whiskers, chopped fiber, or random mat.